The present invention relates to a method for forming a film, and more particularly, to a method for forming a compound film of uniform thickness containing metal, silicon, and nitrogen for use in semiconductor devices on a substrate.
In the manufacture of semiconductor devices, a sputtered film of titanium nitride (TiN) is currently used as a diffusion barrier metal to prevent the diffusion of a metal interconnect into a silicon single crystal or an insulating layer. Additionally, the TiN is also used as a glue layer material to enhance adhesion when tungsten is used for forming an interconnect structure. However, a TiN film formed by sputtering or chemical deposition tends to have a columnar crystal structure, causing a problem that the metal interconnect material easily diffuses along its grain boundary. If a tungsten layer is formed on a TiN glue layer, the tungsten source gas WF6 also easily diffuses along the grain boundary of the TiN layer to cause damage to the TiN glue layer.
Such problems can be alleviated by using a nano-crystalline material with extremely small grains or an amorphous material as a diffusion barrier material. A three-component nitride containing silicon and a refractory metal such as titanium, tantalum or tungsten is promising for such material.
With the trend to continue to miniaturize semiconductor integrated circuits to achieve submicron feature sizes, the width of an interconnect line becomes smaller and the aspect ratio of a contact hole becomes higher. Sputtering method is inadequate to form a film of a uniform thickness on such a structure because the method has a certain directivity. Accordingly, it is required that a uniform film of about 10 nm thickness is formed on a surface having holes of high-aspect ratio, that is, on an extremely uneven surface even using other deposition methods. Although chemical deposition is typically used to form a uniform thickness film, good step coverage can not be obtained under a chemical deposition condition that deposition sources react violently in gas phases. Particularly in the case of using alkylamido metal compound to chemically deposit a metal nitride film, the deposited metal nitride film has a bad step coverage due to the reaction between gaseous alkylamido metal compound and ammonia gas.
Unlike conventional chemical deposition methods where thin film sources are simultaneously supplied on a substrate, the sequential deposition method where the sources are sequentially supplied on a substrate enables formation of a uniform thickness thin film because it can be formed only by chemical reaction of the substrate surface. This method is well described in the following book; T. Suntola and M. Simpson eds., Atomic Layer Epitaxy, Blackie, London, 1990. However, the applications of this method have been limited to the formation of a two component film or a composite oxide film containing more than three components.
Accordingly, it is an object of the present invention to provide a method for forming a three-component nitride film containing metal and silicon for use in a barrier layer which effectively prevents the diffusion of metal interconnects of semiconductor devices.
Another object of the present invention is to provide a process by which a three-component nitride film containing metal and silicon is formed with a uniform thickness despite unevenness of a semiconductor substrate surface.
In order to accomplish the aforementioned object, the present invention provides a method for forming a three-component nitride film containing metal and silicon on a substrate, the method comprising the steps of: (a) preparing separate reactive gases each including at least one selected from the group consisting of a gaseous metal compound, a gaseous silicon compound and an ammonia gas under conditions such that the gaseous metal compound and the ammonia gas does not form a mixture; (b) determining a sequential gas supply cycle of the reactive gases so that supplies of the gaseous metal compound, the gaseous silicon compound and the ammonia gas are each included at least once within one gas supply cycle; and (c) applying the reactive gases to the substrate by repeating the gas supply cycle at least once.
The reactive gases include only five types of gases such as a gaseous metal compound, a gaseous silicon compound, an ammonia gas, a mixture of a gaseous metal compound and a gaseous silicon compound, a mixture of a gaseous silicon compound and an ammonia gas because gaseous metal compound and the ammonia gas react each other thus should not form a mixture.